Epoxy resins are used in extensive fields of electrical and electronic materials, sealing materials, coating materials, adhesives, civil engineering and construction materials, composite materials for aerospace and the like, because epoxy resins are well-balanced in properties such as electrical properties, resistance to humidity, resistance to heat, mechanical properties, adhesion to molded products produced by insert molding and also because it is possible to provide an epoxy resin composition which are imparted various properties by inclusion of other components.
For example, although metals, ceramics, phenolic resins, silicone resins or the like have been used as an encapsulating material for elements of electronic parts such as LSI, VLSI and the like, epoxy resins are frequently used in recent years because of economy, productivity and well-balanced properties.
On the other hand, it is mandatory for electronic parts having LSI, VLSI or the like to have flame retardancy which complies with UL standard in order to assure safety. For this reason, halogen compounds, antimony trioxide, metal hydroxides or like flame retardants are mixed with an epoxy resin.
However, an epoxy resin mixed with a halogen compound has a drawback that a poisonous gas and a toxic compound are generated on combustion of a molded product of such epoxy resin.
Further, the use of antiomony trioxide which is presumably carcinogenic is undesirable. Moreover, an epoxy resin mixed with antimony trioxide lowers the arc resistance of a molded product of epoxy resin, resulting in reduced insulating property.
In addition, metal hydroxides such as aluminum hydroxide or magnesium hydroxide can not exhibit the desired flame retardancy unless mixed with an epoxy resin in a large amount. Thus the metal hydroxide presents a problem of decreasing the mechanical property of the obtained molded product of epoxy resin.
To overcome these problems, a technique was developed in which an epoxy resin is mixed with red phosphorus, phosphates, organic phosphorus compounds or like phosphorus compounds.
Japanese Unexamined Patent Publications No. 100108/1996, No. 151427/1996, No. 151505/1996 and No. 287795/1998 disclose flame-retardant epoxy resin compositions containing red phosphorus. However, red phosphorus reacts with a small amount of water, giving phosphine and corrosive phosphoric acid. Consequently a flame-retardant epoxy resin composition containing red phosphorus is problematic in respect of resistance to moisture. For this reason, the flame-retardant epoxy resin composition containing red phosphorus can not be used as an encapsulant for a semiconductor which requires high resistance to moisture. Red phosphorus particles coated with aluminum hydroxide, thermosetting resin or the like unavoidably give phosphine and corrosive phosphoric acid on reaction with a small amount of water, resulting in insufficient moisture resistance.
Japanese Unexamined Patent Publication No. 43536/1999 discloses a flame-retardant epoxy resin composition containing phosphate. However, phosphate is low in moisture resistance and thus the disclosed flame-retardant epoxy resin composition can not be used as an encapsulant for a semiconductor.
Japanese Unexamined Patent Publications No. 11662/1992, No. 230340/1993, No. 214068/1993, No. 80765/1994, No. 188638/1996 disclose flame-retardant epoxy resin compositions containing an organic phosphorus compound. However, the organic phosphorus compounds used in these patent publications raise problems about toxicity. Furthermore, molded products formed from each of the epoxy resin compositions disclosed in these patent publications are unsatisfactory in heat resistance and moisture resistance.
In addition, an epoxy resin composition containing a phosphazene compound as a flame retardant has been known. For example, Japanese Unexamined Patent Publications No. 120850/1986, No. 349/1988, and No. 259292/1998 and Japanese Examined Patent Publication No. 53787/1994 disclose flame-retardant epoxy resin compositions containing a phenoxyphosphazene compound. Further Japanese Unexamined Patent Publication No. 109346/1987 and Japanese Patent No. 2857444 disclose epoxy resin compositions containing a fluorine-containing phosphazene compound.
However, these epoxy resin compositions containing a phosphazene compound are not satisfactory in all of heat resistance, thermal impact resistance, solder crack resistance (heat resistance of solder) and moisture resistance which are required by an encapsulant for a semiconductor such as VLSI.
In view of the above, there is a demand for development of an epoxy resin composition which is satisfactory in all of heat resistance, thermal impact resistance, solder cracking resistance (heat resistance of solder) and moisture resistance required by an encapsulant for a semiconductor such as VLSI, the epoxy composition being suitably used as an encapsulant for a semiconductor.